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#1 Ed Jones

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Posted 10 December 2009 - 11:44 AM

Here's another platform I made with a removeable laser fixture for polar alignment. Ready to varnish.

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#2 Don H

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Posted 10 December 2009 - 01:15 PM

Absolutely beautiful, Ed! Can you post some dimensions and details about motors and construction? I'd really like to make my own platform, but the electronics part intimidates me. I wish somebody just sold a motor set-up ready to go with like a 9 volt battery...

http://donscopes.webs.com/

Best of luck,
Don

#3 Ed Jones

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Posted 10 December 2009 - 01:43 PM

This one was made just like this one I made before. It uses 4RPH AC synchronous motors, no electronics, just plug them into line current or use an inverter. These motors are clockwise instead of counter-clockwise so they have to go in the front and drive 1/2 inch SS shafts. The top measures 27.5 inches wide, sides are 24 inches long and the back is 16 inches. Sector sag is 4.5 inches, platform height is 4.75 inches and tracks for 1 hour and 15 minutes. Here's a shot of the motor.

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#4 Leibowitz

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Posted 14 February 2013 - 09:53 AM

Has anyone made this platform or something similar? I love the simple design but I'm looking for a little help with it. I'm looking for an alternative way to cut the bearings. I don't really have the tools to do it the way Ed did his. Or any information about the motors? Seems 1 could use 1 instead of 2.

#5 Ed Jones

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Posted 14 February 2013 - 10:24 AM

The motors are available from Herbach and Rademan. You could use just one with an idler but requires more attention to getting the COG right. I use 2 because they are cheap and allow you to use any scope on it as long as it doesn't tip over.

#6 Leibowitz

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Posted 14 February 2013 - 11:47 AM

I suppose I could make an idler out of something I've got laying around. I see the motor on the Herbach website, I'm just a little confused as to the most effective way to power it. Mechanical I can handle, I've not dabbled in electronics in the slightest. Is there not a way to power the motor while containing it underneath the platform? Running a power cord seems like it would be a PITA. Although, I am trying to keep it cheap.

#7 Ed Jones

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Posted 14 February 2013 - 12:32 PM

Harbor Freight sells a $17 inverter than runs on 12 volts.

#8 Bill Kocken

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Posted 14 February 2013 - 01:01 PM

Ed, Do you determine your sector radius and the drive shaft radius appropriately so that 4RPH is pretty close to 1 RPD? Then you don't have to worry about speed control. Sure saves a lot of complications.

#9 Ed Jones

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Posted 14 February 2013 - 01:18 PM

Correct, with 4 RPH the ratio of the shaft diameter to the bearing radius is 48.87. I use 1/2 inch shafts so the bearing is 23.93 in.

#10 Bill Kocken

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Posted 14 February 2013 - 01:25 PM

Where do you get the 1/2" SS shaft? I see that the motor comes with a 1/8" shaft, with a flat.
I see a project in my future....
So much simpler than my tangent arm / stepper motor driven platform.

#11 Ed Jones

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Posted 14 February 2013 - 02:29 PM

You can get it here , McMaster-Carr or Newport Optical posts work too.

#12 Leibowitz

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Posted 14 February 2013 - 04:44 PM

I'm in over my head here, I'm afraid. But I don't really care. This design seems to be the most straight forward that I've found and I'm definitely set on building it. A few questions still though. I don't understand what the inverter is doing for me. How do I power the motor? Are you plugging the inverter into your car? I'm right at 40 lat so I can use the exact dims as Ed's. I can Macgyver some solution to make the wood cuts I think. Changing out from the 1/8" to 1/2" shaft though, how do you retrofit the 1/2"? I'm also wondering what else I may be able to use for the 3 rollers? I'm not finding anything like that.

#13 Jeff2011

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Posted 14 February 2013 - 05:29 PM

Ed, you do beautiful work. I wish my woodworking skills were as good as yours.

I built my platform with a tangent drive with DC motors. I built a speed control from a kit that I bought from a local electronics shop. I like the AC motors you use with the direct drive, but I was unsure about modifying an inverter. I am dabbling in AP and so far and have been able to get 8 to 10 second exposures at prime focus with my setup and still have fairly round stars. Have you tried AP on your platform with a modified inverter and if you have, how well did it perform?

Thanks,

Jeff

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#14 Ed Jones

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Posted 14 February 2013 - 07:03 PM

The radius of the north bearing is determined by the drawing based on COG. Once you have that you can select the motor speed and shaft diameter to go with it. Different motor speeds are available and I like to match the shaft diameters with available steel diameters and drill sizes to keep things simple. I plug the inverter into a B&D power pack when I don't have house power. I use ball bearing for rollers.

Jeff,
I've dabbled a little in AP but I don't have dark skies. The platform does very well for that though. Mostly I've set my camera and telephoto on a tripod on the platform to take unguided shots. The resistor in the Harbor Freight inverter I converted BTY is R42 but it's tiny. It's 115K and you just need to switch in more and less resistance to change the speed.

#15 wirenut

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Posted 14 February 2013 - 08:24 PM

I used a tangent arm and 12VDC motor. at first I used a model railroad powerpack/transformer to control it. then I picked up a LM 317 regulator ,double pole double throw switch for reverse and a couple of safety switches. Then I made cables to hook up 18V cordless tool batteries and some other cables for various other sources. No hassle of building circuit board and I'm good for many power sources; house,cordless tools,car and many more.

#16 Jeff2011

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Posted 14 February 2013 - 09:49 PM

Thanks Ed.
I could convert my platform to direct drive. I found the hardware I would need at sdp-si and a 2 rph ac sync motor at herbach and rademan would get me close, but I would need to modify an inverter to get the tracking right. I would also need to mount the clockwise motor in front of the sector which would be challenging for my current platform design. However I would only want to do this conversion if I can get better tracking than I do now. Last night I took 37 eight second exposures at 1200mm focal length but only 18 were keepers. I was curious what other people have been able to do with AP on a direct drive platform. I realize the limitations of what I am trying to do. From what I have read on CN, unguided AP is generally limited to 30 seconds even on the best mounts. I just want to maximize what I have and would be happy if I could get consistent 15 second shots.

#17 Ed Jones

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Posted 15 February 2013 - 09:30 AM

Jeff,
I have one platform that I built with a tangent drive and DC motor. I figured out how to make worm gear sectors out of delrin so then then I converted it to a worm sector drive. It works great but my direct drive platforms are just as good or better. Maybe a worm drive would work for you; the speed is constant and there's no linkage backlash as with tangent drives.

#18 cheapersleeper

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Posted 15 February 2013 - 09:45 AM

Jeff,
I have one platform that I built with a tangent drive and DC motor. I figured out how to make worm gear sectors out of delrin so then then I converted it to a worm sector drive. It works great but my direct drive platforms are just as good or better. Maybe a worm drive would work for you; the speed is constant and there's no linkage backlash as with tangent drives.


I think a worm drive of some sort would be a good choice for those of us who, ahem, are a bit imprecise in our workmanship.

Regards,
Brad

#19 Jeff2011

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Posted 15 February 2013 - 10:42 AM

Yes, I think the threaded rod is causing some slop. I did tighten things up by cutting a slot in each end of the coupling nut and squeezing down on it with a vise. This was a recommendation given to me by a machinist and it has helped.

Ed, not sure I follow with the worm gear sector. But it sound like it would be more work than going to a direct drive.

If I do go to a direct drive, would I need two AC motors like on your platform? I currently use one DC motor to drive the platform and the other to rewind. The scope is about 40 lbs. Do you have any issues with sector slipage?

Thanks,

Jeff

#20 Bill Kocken

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Posted 15 February 2013 - 10:56 AM

Ed,
I looked at the SS shafts at Mcmaster Carr and your other sites, but I didn't see any that were bored to fit over the motor's 1/8" drive. How did you do that? I have a brother-in-law with a machine shop, but I know SS very hard to drill.

#21 Jeff2011

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Posted 15 February 2013 - 11:48 AM

Bill,

You might want to check out https://sdp-si.com/eStore/

If all else, you could get a rod and a coupler that links the rod to the 1/8 drive.

#22 Ed Jones

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Posted 15 February 2013 - 12:21 PM

Jeff,
It can work with one motor see my post above. Slippage isn't an issue as long as the platform runs correctly with nothing rubbing or binding. I get good traction with wood or laminate covered bearings which take more abuse. Here's my sector mounted behind my bearings.

Bill,
No you won't find shafts with an 1/8 inch hole, my son-in-law has a lathe and does mine. Brass can work too, easier to work but tarnishes.

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#23 Jeff2011

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Posted 15 February 2013 - 01:41 PM

Thanks for posting the worm drive picture and the advice Ed.

I will probably stick with what I have for a while and maybe down the road take a crack at converting to direct drive.

I don't have anything binding or rubbing. Which was quite a suprise that I was able to accomplish that. I use good quality skateboard bearings and the platform moves very smoothly. The bottom of my sectors are covered with an aluminum strip. I supose I would need to ruffen that up on one side so that the roller could get a good grip. The roller I found matches my skateboard bearing diameter so it should be a simple replacement of one of my bearings. Hooking up the motor on the front will be the challenging part though.


Thanks again for all your help and advice. Building the platform was a fun and challenging project that took a lot of thinking and planning in addition to careful and hard work. I was able to incorporate a lot of ideas from other peoples platforms (including yours Ed) and came of up a design that worked for me. In the end, I am very pleased with it. It is definately sutiable for webcam style planetary AP and visual as it stands today.

#24 davidpitre

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Posted 15 February 2013 - 09:46 PM

I know this is ATM, but for those that don't know, Ed sells these platforms downright cheap. I am thrilled with mine.

#25 cheapersleeper

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Posted 15 February 2013 - 11:01 PM

Good to hear you like it. My friend in TAS up here in Dallas just got one but I have not yet seen it in action. Looking forward to seeing the work of the esteemed Mr. Jones in person.

B






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